One technique for providing a plastic skin on the surface of a plastic foamed body is a process of forming a skin by rotational molding, subsequently pouring and foaming polyurethane in the skin. By this process, however, the skin and the core do not adhere together, resulting the flexural strength and the impact strength to be not satisfactory. Further, the processing temperature of a product is low, and then strain exists in the shaped body, causing the deformation with time, furthermore, the product is composed of two different materials, and then recycling is difficult. In addition, the process consists of two steps, which causes an increase in the cost, and such means that foaming of the skin or providing reinforcing members in the core is difficult. Another technique is a process consisting of forming a skin by blow molding, filling in it with foam particles, and heating them. In this technique, it is difficult to conduct the heating at high temperatures, consequently, voids tend to develop between core particles. In addition, molding is conducted at low temperatures, causing the adhesion between the skin and the core to be unsatisfactory, strain to remain in the shaped body, and resulting the flexural strength and the impact strength to be low, deformation to occur with time, furthermore, such means that foaming of the skin or providing reinforcing members in the core are difficult, and a large size shaped body cannot be produced.
A technique for producing a composite consisting of a skin and a foamed body, by charging plastic powders and pellets that can be cross-linked and foamed in a mold, subsequently by conducting rotational molding, was invented by one of the inventors of the present invention approximately 30 years ago (U.S. Pat. No. 3,814,778 and U.S. Pat. No. 3,914,361). According to this technique, a skin and a core are formed in a same step, allowing the skin to be excellently adhered to the core, consequently, the flexural strength and the impact strength of the shaped body to be improved. However, it is difficult to produce a shaped body with a skin of an even thickness and a highly foamed core, and with almost no void in a stable condition, which results that this technique has not been practically applied up to now.